Various efforts have hitherto been made to increase the functionality of polymeric compounds. For example, in one approach currently used to increase the refractive index of polymeric compounds, aromatic rings, halogen atoms or sulfur atoms are introduced onto the compounds. Of such compounds, episulfide polymeric compounds and thiourethane polymeric compounds, both of which have sulfur atoms introduced thereon, are in practical use today as high-refractive index lenses for eyeglasses.
The most effective way to achieve even higher refractive indices in polymeric compounds is known to involve the use of metal oxides. For example, a method for increasing the refractive index by using a hybrid material composed of a siloxane polymer mixed with a material containing small dispersed particles of zirconia, titania or the like has been disclosed (Patent Document 1).
A method in which a condensed ring skeleton having a high refractive index is introduced onto portions of a siloxane polymer has also been disclosed (Patent Document 2).
Numerous attempts have been made to impart heat resistance to polymeric compounds. Specifically, it is well known that the heat resistance of polymeric compounds can be improved by introducing aromatic rings. For example, polyarylene copolymers with substituted arylene recurring units on the backbone have been disclosed (Patent Document 3). Such polymeric compounds show promise primarily in use as heat-resistant plastics.
Melamine resins are familiar as triazine resins, but have very low decomposition temperatures compared with heat-resistant materials such as graphite.
The heat-resistant organic materials composed of carbon and nitrogen that have been in use up until now are for the most part aromatic polyimides and aromatic polyamides. However, because these materials have linear structures, their heat-resistance temperatures are not all that high.
Triazine-based condensation materials have also been reported as nitrogen-containing polymeric materials having heat resistance (Patent Document 4).
In recent years, there has arisen a need for high-performance polymeric materials in the development of electronic devices such as liquid-crystal displays, organic EL displays, optical semiconductor devices (LEDs), solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors.
The specific properties desired in such polymeric materials include (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, and (5) low volume shrinkage.
The inventors earlier discovered that hyperbranched polymers containing recurring units with a triazine ring and an aromatic ring have a high refractive index, are capable of achieving, with the polymer alone, high heat resistance, high transparency, high refractive index, high solubility and low volume shrinkage, and are thus suitable as film-forming compositions in the manufacture of electronic devices, and that such compositions can be utilized as embedding materials on organic EL devices and photodiodes (Patent Document 5). However, cracks tend to arise in embedding layers produced from such compositions, and so there has been a desire for a solution to this problem.
Top emission-type organic EL devices which extract light from the opposite side of the substrate (top electrode side) generally have a structure in which are formed, in order, a substrate/a metal electrode/an organic EL layer/a transparent electrode/a sealing layer such as glass. To further increase the light-extracting efficiency, a high refractive index layer is sometimes formed as a light-extracting layer between the transparent electrode and the sealing layer.
However, because the light-extracting layer-forming compositions that have hitherto been used contain solvents, when the light-extracting layer is formed, the organic EL layer degrades under the influence of the solvent.